There are many valuable deposits or sub-surface production reservoirs located 400-1000 feet below the surface of the earth which cannot be mined or produced economically by the employment of conventional mining or production techniques. In such an instance, it would be advantageous to be able to form a borehole which extends vertically downwardly and then turns laterally towards the horizontal such that the lateral portion of the borehole is extended a considerable distance through the ore body. The lateral portion of the borehole enables various different chemical treatments to be carried out, thereby enabling the mineral values to be extracted therefrom.
It is known to form a vertical borehole and to turn the borehole 90.degree. such that the borehole extends a limited horizontal distance from the vertical borehole. The Zublin curved drilling method provides a reliable and highly accurate means by which straight drilling beyond the curve can be carried out for a limited distance. The following U.S. patents are considered of significance respective to the drilling of wellbores which are deviated from the vertical into the horizontal plane:
______________________________________ U.S. Pat. No. Date of Issuance Title ______________________________________ 2,699,920 Jan. 18, 1955 Apparatus for drilling laterally deviating bores from a vertical bore below a casing set therein 2,708,099 May 10, 1955 Flexible resilient norm- ally curved tubular drill guide having fric- tion shoes 2,717,146 Sept. 6, 1955 Heavy duty flexible drill pipe 2,734,720 Feb. 14, 1956 Apparatus for drilling wells with oriented curved bores of large radii 2,734,082 April 24, 1956 Method of drilling de- viating bores from existing wellbores 2,745,634 May 15, 1956 Apparatus for drilling wells with oriented curved bores of large radii 2,745,635 May 15, 1956 Apparatus for drilling wells of large radii curved bores 2,804,926 Sept. 3, 1957 Perforated drain hole liner ______________________________________
However, none of the above cited prior art references disclose the concept of drilling a vertical hole into proximity of a pay zone or production reservoir, turning the lower end of the hole to a desired angle with the curve having a small radius of curvature, and thereafter, continuing the borehole in a straight line laterally away from the vertical part of the borehole for an extended distance while penetrating the pay zone.
One of the problems frequently encountered in utilizing the Zublin drilling technique is that the lateral distance that can be drilled after deviation from the vertical is very limited because of the problems encountered in turning the drill bit under pressure. There are in existence in the prior art some devices which aid in solving this problem. These include mud powered turbine drilling devices such as the "turbodrill" produced by Maurer Engineering, Inc., and electric powered drills such as the "electro drill" produced by the Institut Francais Der Petrole. However, these devices have been only marginally successful because of their relatively large size, complexity, difficulty in operation, and in the case of the electric drill, its need for a nearby source of electricity.
The solution of these as well as other problems is the subject of this invention.